This addresses two bugs
1. Fullscreen icon being visible with audio files
2. No poster image being visible with audio files
The fix is to store the type of media in our mediaModel, and ensure the view
reflects this state as a flag jw-flag-media-audio.
When this flag is present we simply apply the necessary styles.
[Fixes #93928228]

Updates to ad skip button. Added some basic style inheritance in the basic-skin-styles mixin and a specific font-size and line-height to make sure the ad skip button doesn't vertically shift in size once the skip icon appears. Skins also add minor corner rounding to skip buttons to make them look more consistent with the rest of the skin
[Fixes #99791878]